I inherited an Apache setup that after years of modifications, needs a bit of a cleanup. Every .html file is processed for both SSIs and PHP. The only active SSI is a virtual include of a CGI script, which is on almost every file. PHP use is more sporadic, used only on a certain fraction of pages (we have thousands of articles). I want to change all <!--#include virtual="..."--> references to use the PHP virtual() function instead and disable SSI parsing. From what I have read, the PHP virtual() function isn't as efficient as the SSI include, but I would expect the disabling of all SSIs to have a great performance increase.

I haven't seen any benchmarks one way or another, just some anecdotal references. Anyone have any other opinions? Here is a small snippet of the Apache 2 config:
...
AddHandler server-parsed .html
AddType application/x-httpd-php php
Options Includes ExecCGI FollowSymLinks
...
<FilesMatch "\.(php|htm?l|)$">
SetOutputFilter PHP
SetInputFilter PHP
LimitRequestBody 524288
</FilesMatch>
...
AddOutputFilter PHP .html
...